Consider updating nibbles fork

[moneylobster]

Trying to build the Mezzano cold image on SBCL 2.5.0 gives an error on these lines of the nibbles fork, saying that sb-vm::make-ea is undefined. The upstream has had a commit removing the use of this function. Can anyone else replicate this error I'm getting in newer SBCL versions? Syncing the fork upstream or transferring over the changes from the relevant commit could fix this.